/**
 * @desc   数组求差集 arr1里面有 arr2里面没有
 * @param  {Array} arr1 
 * @param  {Array} arr2 
 * @return {Array} 
 */
export function difference(arr1,arr2=[]){
    if(arr1.length === 0){
        return []
    }
    if(arr2.length === 0){
        return arr1.slice();
    }
    const result = arr1.filter(item => !arr2.includes(item))
    return result
}